In the art of laying pipeline, whether for above ground or inground installation, individual pipe sections must first be joined, e.g. by welding. Thereafter, it is common practice to apply a protective wrap over the seam where the pipes are joined. The protective wrap may be in the form of a tube or sleeve which is slipped over the seam or it may be in the form of a sheet material or tape which is wound over the joint and secured in place. In either case, the inner surface of the wrap may contain an adhesive layer to enhance maintaining the protective wrap in place, as well as adherence to any irregularities in the pipe surface.
It is well known in the art to employ so-called heat-shrinkable or heat-recoverable materials for these protective wraps. While the patent literature is replete with references to heat-shrinkable materials for this purpose, the following patents selected from, cursory search may be taken as illustrative.
U.S. Pat. No. 3,847,721 issued to Evans discloses articles for protecting tubular conduits which are heat recoverable in involute fashion to an overlapping, generally cylindrical configuration.
U.S. Pat. No. 4,517,234 issued to Fisher relates to flat lengths of heat recoverable material with integral latching means so that the material may be wrapped around a cable, pipe or similar structure, latched together and then shrunk down onto the structure by heating.
U.S. Pat. No. 4,521,470 issued to Overbergh discloses a dimensionally heat recoverable article useful for protection of service lines such as oil pipes and district heating pipes against corrosion, which articles carry a thermoplastic polymeric material and a heat-softenable adhesive of smaller thickness and lower softening or melting point than the polymeric material.
A particularly efficacious heat-shrinkable pipewrap material is described and claimed in the copending application of Anthony J. Doheny, Ser. No. 003,091 filed Jan. 14, 1987, and assigned to the Kendall Company, assignee of the instant application. As described therein, a polyolefinic film is oriented by stretching in the machine direction and thereafter a surface of the oriented film is irradiated with a low energy electron beam to provide a controlled differential crosslinking throughout its thickness from the irradiated surface, the degree of crosslinking thus decreasing from the irradiated surface to where substantially no crosslinking occurs at the opposed surface. Preferably, an adhesive layer, e.g. a rubber-based adhesive, is applied to the non-irradiated surface at some stage in the manufacturing process to provide a heat shrinkable adhesive tape which may then be spirally wound over the pipe joint.
Irrespective of whether the heat shrinkable protective pipewrap is initially in the form of a sleeve, a sheet of flat material or an adhesive tape, it is positioned over the pipe joint, typically extending on the order of one foot or more on either side of the seam, and then heat is applied circumferentially around the surface to effect shrinking so that the wrap is tightly adhered to prevent corrosion or other degradative environmental forces.
Typically, this is done by the pipeliner with a torch. In order to heat the underside, i.e. what may be described as the 4-8 o'clock portion of the circumference, it is necessary for him to be on the ground and/or under the pipe.
Apart from the time, effort and inconvenience for this method of application, heat applied sequentially in this manner is frequently inconsistent and non-uniform.
Stated simply, the task of the present invention is to obviate these disadvantages and to provide a method for easily and efficiently providing the consistent heat required for uniform shrinking of the protective wrap around the pipe circumference.